Your previous version of the Web AppBuilder installation directory is similar to C:\arcgis-web-appbuilder-1.0. The app ID is 2 for the app at http://[your host name:port number]/webappbuilder/apps/2/.

Once the upgrade is complete, start the new version of Web AppBuilder to check the result. You should see all your upgraded apps.

If the upgrade failed, see the upgrade.log file in the \server\logs directory of the Web AppBuilder installation.

Running the command multiple times will upgrade and import apps multiple times into the new version of Web AppBuilder. This is by design.

If you have custom widgets and themes in the app that were created in the previous version of Web AppBuilder, the command utility will import them into the new version as well, without automatically checking them. You need to make sure these custom widgets are compiled with the version of ArcGIS API for JavaScript and version of Web AppBuilder to which you import the app. See the version comparison chart.